Money was a professor of pediatrics and medical psychology at Johns Hopkins University from 1951 until his death. While there Money was involved with the Sexual Behaviors Unit, which ran a sex reassignment surgery (the program was closed in 1979. The present day version of this unit is the Johns Hopkins Sexual Behaviors Consultation Unit, or SBCU).[2] He is also known for the controversial case of David Reimer. Money reported Reimer was successfully reassigned as a female in infancy after a botched circumcision, then failed to report that the reassignment was actually not successful in the long term.

Money was an early supporter of New Zealand's arts, both literary and visual. He was a noted friend and supporter of author Janet Frame. In 2002, as his Parkinson's disease worsened, Money donated a substantial portion of his art collection to the Eastern Southland Art Gallery in Gore, New Zealand.[4]

Money's definition of gender is based on his understanding of sex differences among human beings. According to Money, the fact that one sex produces ova and the other sex produces sperm is the irreducible criterion of sex difference. However, there are other sex-derivative differences that follow in the wake of this primary dichotomy.

These differences involve the way urine is expelled from the human body and other questions of sexual dimorphism. According to Money's theory, sex-adjunctive differences are typified by the smaller size of females and their problems in moving around while nursing infants. This then makes it more likely that the males do the roaming and hunting. Sex-arbitrary differences are those that are purely conventional; for example, color selection (baby blue for boys, pink for girls). Some of the latter differences apply to life activities, such as career opportunities for men versus women.

Finally, Money created the now-common term, gender role, which he differentiated from the concept of the more traditional terminology, sex role. According to Money, the genitalia and erotic sexual roles were now, by his definition, to be included under the more general term "gender role;" including all the non-genital and non-erotic activities that are defined by the conventions of society to apply to males or to females.

Money made the concept of gender a broader, more inclusive concept than one of male/female. Now, gender includes not only one's status as a man or a woman, but as a matter of personal recognition, social assignment, or legal determination; not only on the basis of one's genitalia but also on the basis of somatic and behavioral criteria that go beyond genital differences.

Gender identity is one's own categorization of one's individuality as male, female, or ambivalent as experienced in self-awareness of one's own mental processes and one's own actual behavior.

Gender role is the public manifestation of one's gender identity, the things that one says and that one does that gives people a basis for inferring whether one is male, female, or fits neither of those categories.

To stress the idea that gender identity and gender role are two aspects of the same thing, Money coined a new term: Gender-Identity/Role, which he frequently abbreviates as "G-I/R."

Money's ideas relating to gender and gender identity formation have come under criticism. Money maintained that a child's gender identity is fluid up to a certain age, after which this gender would become consolidated and more-or-less immutable. This theory was applied in the case of a male child, David Reimer, whose penis was destroyed due to a botched circumcision. This came to be known as the John/Joan case.[6] The child was subsequently sexually reassigned as female. However, even though David Reimer was raised as a girl and never knew his early history, he behaved in a masculine way appropriate to a boy while he was a young child. Later attempts to socialize him as a girl failed. Money knew this yet never revealed this information for years. He was eventually exposed in 1997 in a paper authored by Milton Diamond and Keith Sigmundson.[7] His decision to "cover up" the facts of the case caused Money great difficulty in the medical community.

As for Reimer, when he finally reached the age to make his own medical decisions, he was so distressed by Money's demand for further surgery to complete his "female" genitals, that his parents decided to reveal his medical history to him. He immediately re-transitioned to a male gender role and later underwent genital reassignment surgery again, in order to complete his male gender identity with male genitalia. He underwent four rounds of reconstructive surgery to facilitate his reappropriation of the male sex. Towards the end of his life he lost his job, was separated from his wife, failed a financial investment, and mourned the suicide of his twin brother Brian. He committed suicide on May 5 2004. John Colapinto, who publicised Reimer's story in a Rolling Stone article[8] and the book As Nature Made Him,[9] speculated that Reimer never psychologically recovered from his childhood trauma:

"David's mutilation and his parents' guilt were tightly entwined, multiplying the mental anguish to which the family members were already prone. [...] David's blighted childhood was never far from his mind. Just before he died, he talked to his wife about his sexual "inadequacy," his inability to be a true husband."[10]

Money claimed that media response to the exposé was due to right-wing media bias and "the antifeminist movement." He claimed his detractors believed "masculinity and femininity are built into the genes so women should get back to the mattress and the kitchen."[11] However, intersex activists also criticized Money, stating that the unreported failure had led to the surgical reassignment of thousands of infants as a matter of policy.[12] Privately, Money was mortified by the case, colleagues said, and as a rule did not discuss it.[13]

It should also be pointed out that the Johns-Hopkins University no longer performs the kind of research and surgeries pioneered by Money due to their lack of a valid scientific basis.[14]

John Money was critical in the debate on pedophilia. He felt that both sexual researchers and the public do not make distinctions between affectional pedophilia and sadistic pedophilia, including infantophilia (occasionally referred to as nepiophilia), pedophilia and ephebophilia. For Money, affectional pedophilia is about love and not sex.

If I were to see the case of a boy aged ten or eleven who's intensely erotically attracted toward a man in his twenties or thirties, if the relationship is totally mutual, and the bonding is genuinely totally mutual...then I would not call it pathological in any way.[15]

His view was that affectional pedophilia is caused by a surplus of parental love that became erotic, and is not a behavioral disorder. Rather, he felt that heterosexuality is another example of a societal and therefore, a superficial, ideological concept.